- Extract the UPDATE partition from an XCI image of the cartridge that contains the update you want into a folder
These are common cartridges and firmware versions they contain:
Puyo Puyo Tetris/ 1-2 Switch (1.0.0) - would never recommend installing this one as no Switch made with 1.0.0 actually runs it (its a slightly different 1.0.0 with exFAT that bricks you)
Dragon Ball Xenoverse 2/ Mario plus Rabbids Kingdom Battle/Cars 3 Driven to Win (2.1.0)
Splatoon 2/ Sonic Forces (2.3.0)
Pokemon Tournament DX (3.0)
Batman The Telltale Series/ Syberia 2/ The Elder Scrolls V. Skyrim (3.0.1)
Attack on Titans 2/ Xenoblade Chronicles 2 (3.0.2)
Bayonetta 2/ Gal Gun 2 (4.0.1)
Kirby Star Allies (4.1.0)
Octopath Traveler (5.0.2)
Taiko no Tatsujin Nintendo Switch Version JPN (5.1.0)
- Copy the SYSTEM:/Contents/registered folder from another Switch that is running the firmware version you want
- Copy the SYSTEM:/Contents folder from a Switch that has a "System update is pending" notification. This will let you pick either the currently running firmware, or the pending firmware to install.
- *cough* xbins *cough*